An anesthetic vaporizer is an apparatus that can be used to effectively vaporize a liquid anesthetic agent, and can precisely input the liquid anesthetic agent at a certain concentration into an anesthesia breathing circuit. The anesthetic vaporizer typically comprises a fresh gas inlet, a pressure compensation unit, a fresh gas cut-off valve, a wick unit, a bypass circuit, a temperature compensation unit, a concentration control unit, a mixed gas outlet, a filling unit, and a vaporizing chamber. The vaporizing chamber is a reservoir for storing liquid anesthetic agent. The wick unit is provided within the vaporizing chamber. A part of the wick unit is immersed into the anesthetic agent such that the wick unit is filled with saturated anesthetic vapor.
After fresh gas flows into the vaporizer through the fresh gas inlet, a part of the gas flows into the wick unit via the fresh gas cut-off valve after passing through the pressure compensation unit. When the fresh gas flows through the wick unit, the fresh gas will be mixed with parts of the anesthetic vapor. The fresh gas carrying the anesthetic vapor flows into the concentration control unit after passing through the wick unit. The other part of the fresh gas flows into the bypass circuit, then flows into the concentration control unit after passing through the temperature compensation unit, and meets the fresh gas carrying the anesthetic vapor in the concentration control unit. By controlling the concentration control unit, the two streams of gases are mixed at a certain ratio of anesthetic gas and outputted out of the vaporizer from the mixed gas outlet.
When the vaporizer is used continuously, the temperature of the vaporizer drops since the anesthetic agent has to absorb heat to vaporize, which in turn reduces the evaporation speed of the anesthetic agent since the evaporation speed of the liquid decreases as the temperature drops. Thus, the concentration of the anesthetic vapor outputted from the vaporizer is reduced accordingly. As the temperature within the vaporizing chamber rises, the pressure of the saturated vapor increases, and then the concentration of the outputted anesthetic vapor will gradually increase.
In order to solve the problem of the change of the output concentration of the anesthetic vapor due to the change of temperature, the flow is typically adjusted by a temperature compensation unit with flow adjustment mechanism. As the temperature within the vaporizing chamber changes, the temperature compensation unit will change the nominal diameter of a valve port thereof to increase or decrease the flow of the dilute gas stream passing through the bypass circuit, such that the concentration output of the vaporizer does not change due to the change of temperature.
A conventional temperature compensation unit, as shown in FIG. 1 comprises an upper valve port assembly and a lower valve port assembly. The upper valve port assembly comprises an upper valve port 46 and a plurality of metal rods 45 having a low temperature linear expansion coefficient. The metal rods 45 are assembled with a copper body 44 having a high temperature linear expansion coefficient. The lower valve port assembly, which is generally in the form of “T”, comprises a lower valve port 47, an upstanding rod 49 and a fixing nut 50. The upstanding pod 49 has the low temperature linear expansion coefficient. The upstanding pod 49 is assembled with a copper valve seat 48 having a high temperature linear expansion coefficient so as to define two temperature sensitive valves. The fresh gas flowing in through the fresh gas inlet 41 enters between the upper and lower valve ports via the bypass circuit 45, and the mixed gas is outputted via the mixed gas outlet 51. When the temperature within the vaporizing chamber changes, both the upper and lower valve ports move relative to their initial positions, so as to change the caliber between the two valve ports, thereby achieving the purpose of temperature compensation.
However, this type of compensation unit has disadvantages, such as the following: (1) the lower valve port assembly, which has a relatively short length, is only immersed into the upper space in the vaporizing chamber while remaining a certain distance away from the bottom of the vaporizing chamber. During the anesthetic operation, when the liquid level of the anesthetic is below the bottom of the lower valve port assembly, the agent will no longer directly contact the metal valve seat of high temperature linear expansion coefficient, which is disadvantageous to heat exchange and reduces the compensation effect. (2) Since the upper valve port assembly is installed with a plurality of metal rods which are required to be adjusted when the vaporizer is calibrated, the structure is complicated, and the requirements for installation and adjustment are accordingly relatively high, causing excessive difficulties and expense for installation and adjustment of the compensation unit.